This document summarizes a study identifying sources of resistance to stem rust in Ethiopian durum wheat landraces. In 2009, 991 landraces were tested for resistance to stem and leaf rust. While most were susceptible to leaf rust, 79.5% showed resistance to stem rust. In 2010, 28 landraces exhibited resistance to both diseases. These landraces provide valuable resistance sources that can be exploited in wheat breeding programs to develop cultivars with resistance to stem rust races like Ug99.

1. Valuable Sources of Resistance in the Ethiopian durum
wheat landraces to Ug99 and other stem rust races
Worku Denbel1* and Ayele Badebo2
1 Ethiopian Institute of Agricultural Research (EIAR), Kulumsa Agricultural Research Center, P.O. Box. 489, Asella, Ethiopia
2 Debre Zeit Agricultural Research Center, P.O.Box 32, Debre Zeit, Ethiopia
*Corresponding author: workudi@yahoo.com
INTRODUCTION
Puccinia. graminis f.sp. tritici is one of the debilitating wheat diseases worldwide. For at least two decades, stem rust of
wheat was considered to be a disease of minor importance mainly due to the incorporation of Sr31 resistance gene in
many of the bread wheat cultivars; however, this gene succumbed to a new stem rust race called Ug99 (TTKSK)
(Pretorius et al., 2000). In Ethiopia, two types of wheat (hexaploid, Triticum aestivum L., and tetraploid, T. turgidum L)
are cultivated under rain-fed conditions mainly by resource-poor farmers. Durum wheat (T.turgidum subsp. durum Desf.)
is the predominating tetraploid, which is an indigenous crop in Ethiopia whereas bread wheat is an introduction, and most
of the high yielding semi-dwarf bread wheat varieties are susceptible to Ug99 and other races prevalent in the country. In
the absence of resistance in cultivated varieties, new sources of resistance are sought from landraces and related species.
Ethiopia is endowed with an immense genetic diversity for tetraploid wheat. All the six species of wheat observed by
Vavilov in the mid-1920s are still grown by farmers as landraces (IBC, 2007). The Ethiopian tetraploid landraces have
been identified to be potential sources of disease resistance including stripe and stem rust (Betesellassie et al., 2007; Haile
et al., 2012).
The high level of diversity in these landraces allows breeders and pathologists to make selection for different traits of
Table 1. The reaction of selected durum wheat
economic importance. Therefore, the major objective of this study was to identify sources of resistance in the Ethiopian landraces to the prevailing stem rust races at Debre
durum wheat landraces to Ug99 and other prevailing races of stem rust at Debre Zeit, Ethiopia. Zeit in 2009 and 2010 seasons.
No. Entries Stem rust severity
MATERIALS and METHODS 2009 2010
(main (off-season)
A total of 991 durum wheat landraces collected from different areas of Ethiopia (Tigray, Gondar, Gojjam, Wollo, Shewa season)
1.
and Kaffa) were used in this study. The collections were made and maintained as single lines by various researchers of 1 WC-1#29 TMR 10MR
1.
durum wheat improvement program of Debre Zeit Agricultural Research Center. The experiment was conducted in 2009 2 WC-1#32 MRMS 15MSS
1.
and 2010 seasons. In 2009 main season, a total of 991 entries were tested whereas in 2010 off-season, 132 landraces 3 WC-1#109 RMR 15MRMS
1.
selected from the main season were used. Each entry was planted in two rows of 1m length together with four checks 4 WC-2#7 TR 20MRMS
1.
(PBW343, Morocco, Ude and Yerer). PBW343 is carrying Sr31 gene (Brama et al., 2003), Morocco (susceptible check), 5 WC-2#12 TR 20MRMS
1.
Ude and Yerer are CIMMYT originated commercail durum wheat varieties in Ethiopia. The nursery was bounded by 6 WC-2#41 TR 20MR
1.
spreader rows planted with mixtures of susceptible durum (Arendeto and local red) and bread wheat (PBW343) varieties. 7 WC-2#80 TR 20MSMR
1.
The spreader rows were inoculated three times starting from stem elongation with mixtures of TTKSK (Ug99) and other 8 WC-2#98 TR 5MRMS
1.
races carrying virulences for stem rust resistance genes including Sr13 using the injection method (Roelfs et al., 1992). 9 WC-2#100 TMR 10MR
Figure 1. Frequency (%) of landraces under different leaf 1.
10 WC-3 #15 TMSMR 10MR
The rust assessment was made three times using the Modified Cobb’s scale (Peterson et al., 1948). The terminal severity rust resistance categories tested at Debre Zeit, 2009 main 1.
11 TR
WC-3 #19 10MRMS
1.
was used to categorize the entries into resistant and susceptible groups. The severity was converted to coefficient of season (N= LR, 991) 12 WC-4 #12 TR 20MSMR
1.
infection (CI) values by multiplying the severity by constant values (Roelfs et al., 1992). The constant values are: R= 0.2, 13 WC-4 #62 TR 20MSMR
1.
MR=0.4, MS=0.8 and S=1. Based on the CI values, the entries were categorized under four resistant groups: The first 14 WC-4 #93 TR 5SMS
1.
group included the landraces with 0-10% severity (resistant), the second with severity 15-20% (moderately resistant), and 15 WC - 12 # 40 TR 15MR
the third with severity of 25-30% moderately susceptible whereas the rest were considered as susceptible. However, only 1.
16 WC - 12 #66 TMS 15RMR
entries which combined leaf and stem rust resistances were advanced to the next stage of evaluation in 2010 off-season. 1.
17 WC -16 #31 TR 10R
1.
18 WC -16 #37 TR 20RMR
1.
RESULTS and DISCUSSION 19 WC -16 #57 TR 15MR
1.
20 WC -16 #145 TR 20RMR
1.
21 DW-A- 4 #12 TMR 5RMR
In 2009 main season, the leaf rust diseases pressure was quite high, and out of the total entries tested, only 4.8% were 1.
22 DW-A-3 #18 TMR 15MR
resistant, 13.2% were moderately resistant, 32.9% were moderately susceptible and the remaining 49.1% were 1.
23 DW-A-3 #20 TR 20RMR
completely susceptible to the disease (Figure 1). Leaf rust has been reported to be the most common disease wherever 1.
24 DW-A-3 #70 TR 20MR
durum landraces are grown (Huluka and Andnew, 1992). In this study, almost all of the durum wheat landraces 1.
25 DW-A-3 #73 TMR 5MS
exhibited susceptible or moderately susceptible reaction to leaf rust; however, they varied in terminal severities. The 1.
26 DW-K-1#57 TR 15MR
absence of complete resistance to leaf rust in the landraces is also in agreement with the previous reports (Andenow et 1.
27 DW-K-1#145 TR 20RMR
al., 1997; Huluka and Andenow, 1992). In Ethiopia, durum wheat and stem rust have co-evolved for thousands of 1.
28 TMR
CD-1-#73 5MS
years and this close association has resulted in the accumulation of a wider virulence spectrum on the side of the rust 29 TMR
Figure 2. Frequency (%) of landraces under different Yerer 30MRMS
(Bechere et al., 1995). The use of durum wheat parents with low level of moderately susceptible or moderately stem rust resistance categories tested at Debre Zeit, 30 5MR
Ude 10MS
resistant infection types is a valuable and a recommended breeding strategy which has been utilized for durum wheat 2009 main season (N= SR, 991) 31 PBW343 50S 80S
improvement in Ethiopia (Bechere et al., 1995) and as a result of such breeding methodology a number of durum
wheat varieties have been released by Debre Zeit Agricultural Research Center.
In 2010 off-season the stem rust pressure was quite high and only 28 landraces were found to be
In 2009 main season, stem rust incidence was relatively low and the highest stem rust severity was 50% on susceptible resistant to stem rust. Those entries showed similar or low levels of stem rust reaction when compared
varieties. Out of 991 landraces evaluated for stem rust resistance, 79.5% exhibited resistance reaction, 10.6% were with the resistant durum wheat cultivars namely Yerer and Ude (Table 1). Out of these, 20 belong to
moderately resistant, 8% were moderately susceptible and the remaining 1.9% was completely susceptible (Figure 2). those collections from Wollo, two from Kaffa, five from Ambo, and one from Chefe Donsa. The stem
The low level of stem rust infection was attributed to the susceptibility of many of the landraces to leaf rust which rust disease pressure is often high in the off-seasons when compared to the main seasons even without
appeared early in the season. Under such circumstances, it was difficult to select for stem rust resistance under field artificial inoculation at Debre Zeit which might be due to favorable (warmer) temperatures in the off-
conditions since the tissue was being killed by leaf rust at early stages. Therefore, only 132 entries which combine season. Probably that was the reason that accounted for the high pressure of stem rust and low
stem and leaf rust resistances have been selected for the subsequent test. frequency of stem rust resistant landraces in the 2010 off-season compared to the 2009 main season.
In this study, combined resistance to stem and leaf rust diseases have been identified in the 28
Ethiopian durum wheat landraces. In previous reports, the Ethiopian durum landraces have been
reported to be excellent sources of stem rust (Bechere et al., 2000) and powdery mildew resistance
(Negassa, 1986). Furthermore, the importance of Ethiopian tetraploid wheat landraces as sources of
resistance to wheat stem rust was reported by Betesellassie et al. (2007). This finding is further
supported by the work of Dyck and Sykes (1995) as they found combined resistances to stem and leaf
rust in the Ethiopian durum landraces. The Ethiopian durum wheat landrace, ST464 carrying Sr7a,
Sr9e and Sr13 genes has been utilized as a source of resistance to stem rust in wheat breeding
programs of many countries (Knott, 1996; Klindworth et al., 2007).
In this study, 28 durum wheat landraces were found to be resistant to leaf and stem rust of wheat with
combined virulence for TTKSK and other races with virulence for Sr13 and Sr9e and the leaf rust
races prevailing in Debre Zeit.
CONCLUSION
The result showed that the Ethiopian durum landraces are potential sources of stem rust resistance and
they could be exploited in wheat breeding programs.
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